This Small Business Innovation Research (SBIR) Phase II project aims to design and construct an ultra-high-resolution, high-precision phase-shift integrated measurement system suitable for metrology of advanced phase-shifting photomasks. A number of semiconductor manufacturers now expect to progress from the 90 nm through the 45 nm nodes using an exposure wavelength of 193 nm. Advanced photolithographic techniques are necessary to print these sub-wavelength features. Phase-shifting photomasks, i.e. those in which the optical thickness, as well as the opacity is controlled, are a key reticle enhancement technology. Fast and accurate metrology of critical-layer phase-shift masks is becoming necessary both for process control and repair validation, but the enabling tools do not yet exist. The goal of this Phase II program is to integrate the actinic high-repetition rate laser built in Phase I into an interferometric laser microscope involving the design, construction, and integration of a stable phase-shifting interferometer and laser microscope, and the incorporation and optimization of phase-shifting interferometry signal processing algorithms. The integrated optical system will enable phase metrology on advanced photomasks, with the measurement precision and spatial resolution required by the International Technology Roadmap for Semiconductors (ITRS), mask makers and mask users.
Commercially, the primary beneficiary of the Phase II photomask phase metrology system is the semiconductor optical lithography industry. The ITRS 'roadmap' for the 90-nm node and beyond requires measurements of photomask optical path difference with sub-0.4 degree precision. This metrology must be performed at spatial resolution scales consistent with feature sizes of the respective technology nodes, and for both isolated and densely-packed structures. No commercial metrology tools yet exist which satisfy these demands. The Phase II high-precision metrology system will enable manufactures to characterize, predict, and control mask-loading effects and other repair and process control issues essential to the reliable fabrication of phaseshifting masks. It is also likely that the integrated phase metrology system will find utility in the area of nano-MEMS testing and other nano-scale interferometry.
